Overcoming a Tight Coil To Give a Random "Co" Polymer Derived from a Mixed Sandwich Cobaltocene
Overcoming a Tight Coil To Give a Random "Co" Polymer Derived from a Mixed Sandwich Cobaltocene
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DOI：
10.1021/ma501323q
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发表时间：
2014-09-23
期刊：
影响因子：
5.5
通讯作者：
Ragogna, Paul J.
中科院分区：
文献类型：
--
作者：
Hadadpour, Mahboubeh;Liu, Yuqing;Ragogna, Paul J.
在多种实验条件下（例如，不同的溶剂、温度、RAFT试剂、浓度和[RAFT试剂]/[引发剂]）。在所有情况下，结果表明，尽管单体在反应过程中被消耗，但所得聚合物的分子量没有显著增加。据确定，随着聚合物链的增长（DP约为10），采用了紧密的线圈形态，这阻碍了额外的，空间要求高的含CpCoCb单体的方法。这导致过早终止/链转移反应，而不是聚合物链长的增加。为了解决这个问题，丙烯酸甲酯（MA）与其较低的空间位阻需求与庞大的CpCoCb的含单体共聚作为间隔。这提供了必要的空间释放和金属聚合物生长的机会。该共聚导致最终材料的多分散性和分子量的显著改善。在随后的实验中，无规共聚物被用作宏观RAFT试剂来制备二嵌段共聚物，具有对分子量的良好控制，允许检查嵌段共聚物在固态下的自组装行为。
Reversible addition-fragmentation transfer (RAFT) polymerization of a eta(5)-cydopentadienylcobalt-eta(4-)cyclobutadiene (CpCoCb) containing monomer under a wide variety of experimental conditions (e.g., different solvents, temperatures, RAFT agents, concentrations, and [RAFT agent]/[initiator]) was examined. In all cases the results revealed that although the monomer was being consumed over the course of the reaction, there was no significant increase in the molecular weight of the resulting polymer. It was determined that as the polymer chain grows (DP approximate to 10), a tight coil morphology was adopted, which hinders the approach of an additional, sterically demanding CpCoCb-containing monomer. This resulted in premature termination/chain transfer reactions rather than an increase in the polymer chain length. To address this problem, methyl acrylate (MA) with its lower steric demand was copolymerized with the bulky CpCoCb-containing monomer to act as a spacer. This provided the necessary steric relief and an opportunity for the metallopolymer to grow. This copolymerization resulted in dramatic improvements in the polydispersity and molecular weight of the end material. In subsequent experiments, the random copolymer was used as a macro-RAFT agent to prepare diblock copolymers, with good control over the molecular weight, allowing for an examination of the self-assembly behavior of the block copolymer in the solid state.